Motorcycles have been used as a means of automotive transportation and as a means of recreation for many years, and throughout much of that time people have modified the conventional two wheel motorcycle structure to provide a third wheel, for additional stability, increased cargo capacity, etc. One of the earliest used modifications involved the addition of a sidecar, which increased the carrying capacity and improved stability in some respects, so long as the motorcycle was traveling in essentially a straight line. One of the major disadvantages of the sidecar, however, is that it decreases stability and control during cornering. Since the sidecar extends from one side of the motorcycle, the resulting structure is non-symmetrical, requiring different control techniques during cornering, depending upon the direction of the turn and the speed of the motorcycle.
Another approach to modification has been to create a tricycle structure by removing the original rear wheel of the motorcycle and replacing it with a pair of rear wheels at each end of a rigid axle. The tricycle configuration is a significant improvement over the sidecar in terms of symmetry and straight line stability, but conventional tricycle designs have continued to experience problems and disadvantages. In the conventional tricycle structure the rigid rear axle is connected to an extension frame that is rigidly attached to the original motorcycle frame, and it is critical that the extension frame and rear axle be correctly aligned in order to track properly as the vehicle is driven. Specifically, the axle must be in essentially perfect perpendicular alignment with the longitudinal axis of the motorcycle frame, and thus with the line of travel of the motorcycle.
The vast majority of three wheel motorcycles are conversions from two wheel motorcycles, constructed from commercially available conversion kits. The conversion systems of the prior art provide non-adjustable rear axle mounting assemblies for connection of a rigid rear axle to the original motorcycle frame. There are two primary functional disadvantages inherent in non-adjustable mounting assemblies: 1. manufacturing control must be very precise with very low tolerance for deviation from exact dimensional specifications (typically within a few thousandths of an inch), and 2. the user of the three wheel motorcycle is unable to adjust the rear axle alignment either during construction or during the useful life of the motorcycle.
There is a further disadvantage associated with the rear axle mounting system of prior art three wheel motorcycle conversion kits. The prior art systems typically utilize a unitary extension frame that connects to the original motorcycle frame at the mounting points for the original rear wheel suspension assembly and extends rearward, with the axle connected to that frame extension. Those extension frames connect to the outside of the original motorcycle frame, thus increasing the width of the three wheel frame between the original frame and the rear axle. The increased width occupies space that would otherwise be available for, e.g., the feel and legs of a passenger, and detracts from the aesthetic appearance of the three wheel design.
There remains a need for a three wheel motorcycle axle mounting system that provides a means for adjustment of the rear axle alignment both during conversion and after, that reduces the cost associated with the high degree of manufacturing precision required for prior art systems, that provides increased passenger room in comparison to prior art systems, and that improves the aesthetic appearance of the converted three wheel motorcycle. It is among the objects of the present invention to provide an adjustable three wheel motorcycle rear axle mounting system. It is also among the objects of the invention to provide an axle mounting system that minimizes interference with available passenger room and that is aesthetically pleasing in appearance. It is further among the objects of the invention to provide a rear axle mounting assembly that may be easily and economically manufactured and easily installed and adjusted. It is additionally among the objects of the invention to provide a rear axle mounting assembly in kit form for conversion of a conventional two wheel motorcycle to a three wheel motorcycle.